Abstract Alzheimer's disease (AD) is a debilitating brain disorder, with staggering human and financial cost. While genetic studies are increasingly identifying polymorphisms that correlate with AD, there still is no clear picture of the molecular and cellular players and the extent to which each contributes to AD. The genetic and molecular complexity of AD and the lack of technology for experimentally unraveling it in human tissues create a bottleneck constricting the discovery of therapeutics and their successful translation into the clinic. Using human iPSCs we recently developed an in vitro blood-brain barrier (iBBB) and deployed it to discover mechanisms causing genetic predisposition to cerebral amyloid angiopathy (CAA). Identical to clinical studies, we found that APOE4, the strongest genetic risk factor for CAA and AD significantly increased amyloid deposition in our iBBB. The tractability of our engineered tissues then enabled dissection of the cellular causes of the disease. We found expression of APOE4 in pericytes alone was sufficient to increase cerebral vascular amyloid accumulation. Pinpointing the causal cells mediating CAA risk then enabled molecular and biochemical studies that established the underlying mechanism and revealed new therapeutic opportunities for mitigating genetic risk of CAA and potentially AD. Here, we will build upon our success, using the iBBB as a scaffold; we will incorporate neurons, oligodendrocytes, and microglia to generate a micro-integrated brain on a chip (miBrain-chip). In UG3 Aim1.1 we will establish miBrain-chips that represent healthy and diseased states of the human brain through iterative rounds of optimization that incorporate state-of-the-art biopolymers and engineering expertise from Robert Langer's lab at MIT. UG3 Aim1.2 will integrate and validate genetically encoded modulators and reporters of neuronal activity enabling the miBrain-chip to investigate how neuronal activity is influenced, and in turn, influences AD pathogenesis. UG3 Aim2 will model the pathological progression of AD in miBrain-chips across cohort of male and female sAD iPSC lines for which we have matched brains samples, clinical history, and genomic sequences. We will build computational models describing the transcriptional, cellular-dynamics and histological transformations that lead up to the end-states of post-mortem AD brains. These longitudinal pathological maps from genetically diverse healthy and sAD individuals will yield mechanistic insight into AD development and create a platform for discovery and efficacy screening of therapeutics. We hypothesize that the mechanisms underlying AD are significantly influenced by genetic variability. In UH3 we will establish the mechanisms underlying APOE4 pathogenesis (UH3 Aim1) and then ascertain the efficacy, toxicity, and therapeutic window of a panel of preclinical and clinical AD drugs using isogenic APOE3 and APOE4 miBrain-chips (UH3 Aim2). Our multimodal strategy will shed light on how genetic variation influences AD pathogenesis and therapeutic response, opening up new avenues for expeditious drug discovery and translation of effective therapeutics to the clinic.